Analysis of the 483 crystals in the Cambridge Structural Database containin
g [AsPh4](+) cations has revealed mutually attractive interactions between
the cations leading to the formation of supramolecular motifs. The types of
inter-cation interaction can be classified by a combination of the C-dista
l-P ... P angle and the angle between C-P-C planes on adjacent interacting
cations. Interactions with a C-distal-P ... P angle of greater than 168 deg
rees indicate a six-fold phenyl embrace (6PE), whilst those at lower angles
form either offset six-fold phenyl embraces (O6PEs) or four-fold phenyl em
braces, which are distinguished by approximately parallel (P4PE) or orthogo
nal (O4PE) C-P-C planes. Of the selected [AsPh4](+) structures. 45% have we
ll-defined intercationic motifs, of which 88% are 6PEs, 8% O6PEs and are 4%
4PEs. This distribution of embrace type is analogous to interactions betwe
en previously studied [PPh4](+) cations. However, the embraces formed by [A
sPh4](+) cations have comparatively longer As As separations, and contain l
ess-well directed local interactions between the component phenyl rings tha
n their phosphonium counterparts. The individual embraces combine to form z
ig-zag chains of 6PEs (ZZI6PEs) or linear chains of O4PEs (LIO4PEs) leading
to either columnar or layered structures. In general, ZZI6PEs form with di
anions, whereas LIO4PEs occur more frequently in monoanionic salts. The cry
stal lattice formed does not depend on anion size. Computation of the energ
ies of attraction between the cations gives values of -3.8, -2.0, -1.8 and
-1.4 kcal mol(-1) for the 6PE, O6PE, P4PE and O4PE, respectively, comparabl
e to the corresponding embraces formed by [PPh4](+) cations. (C) 2000 Elsev
ier Science S.A. All rights reserved.